TEACHER TRAINING NETWORK FOR IRAQ
Instructional Design Template
Subject _______Physics Education_______
Topic ____ _Waves____
Component
Introduction
Content (text)
Physics can be taught purely as a set of laws and definitions; as a series of equations which
are derived from first principles and which are applied in solving mathematical problems.
Alternatively, physics can be taught by providing opportunities for students to create, test
and use concepts (hypotheses), both inductively and deductively. This applies not only to
laboratory work but also to traditional mathematical problem solving. In this way physics
can be made interesting, relevant and challenging. Every teacher knows the sense of
satisfaction to be gained from giving a class that is well prepared and well presented and that
holds the students’ attention from start to finish. This lesson plan has three different kinds of
content: the physics of waves, the natures of science and scientific reasoning, and the
pedagogy of instruction.
TEACHER-LEARNER EXTENSION
Physics, like all other sciences, involves describing, predicting and explaining
nature in the simplest way possible. In general, physics is based on measurement,
so the empirical work comes first and the development and testing of concepts
(especially theoretical concepts and models) follows. Throughout any science
course, the nature of scientific knowledge and scientific reasoning should be
embedded within all topics. See the other lessons that relate to knowledge about
science.
Waves
As a basis for demonstrating an understanding of this concept, students will be able to:

explain how waves carry energy from one place to another.

identify transverse and longitudinal waves in mechanical media, such as springs and ropes,
and on Earth (seismic waves).

solve problems involving wavelength, frequency, and wave speed.

describe how sound is a longitudinal wave whose speed depends on the properties of the
medium in which it propagates.

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classify radio waves, light, and X-rays according to their different wavelength bands in the
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spectrum of electromagnetic waves whose speed in a vacuum is approximately 3 x 108 m/s

identify the characteristic properties of waves: reflection, refraction, diffraction, interference,
Doppler effect, and polarization
Properties of Light
As a basis for demonstrating an understanding of this concept, students will be able to:

identify visible light as a small band within a very broad electromagnetic spectrum.

explain how for an object to be seen, light emitted by or scattered from it must be detected by
the eye.

recognize that light travels in straight lines if the medium it travels through does not
change.

demonstrate how simple lenses are used in a magnifying glass, the eye, a camera, a telescope,
and a microscope.

perform an experiment that shows that white light is a mixture of many wavelengths
(colors) and predict how retinal cells react differently to different wavelengths and create
the sense of colour vision.

perform an experiment that demonstrates how light can be reflected, refracted, transmitted,
and absorbed by matter.

design an experiment that demonstrates that the angle of reflection of a light beam is equal
to the angle of incidence.
TEACHER-LEARNER EXTENSION
Notice the use of specific directions in the list of outcomes for students listed above;
e.g., “explain”, “perform” and “identify”. These directing words make it clear to
students what is expected of them. These words also direct the teacher when making
test items for a formative or summative assessment tool.
Purpose
The general aim of education is to contribute towards the development of all aspects of the
individual, including aesthetic, creative, critical, cultural, emotional, expressive and
intellectual, for personal and home life, for working life, for living in the community and for
leisure. The education programmes are presented within this general aim, with a particular
emphasis on the preparation of students for the requirements of further education or training,
for employment and for their role as participative, enterprising citizens.
All Leaving Certificate programmes should aim to provide continuity with and progression
from the Junior Certificate programme. The relative weighting given to the various
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components; e.g., personal and social (including moral and spiritual) development,
vocational studies and preparation for further education and for adult and working life within
the programmes, may vary.
More specific to this topic the pedagogic purpose is:

To widen the teacher-learner repertoire of teaching and assessment methods
participants are competent to use.

To support teacher-learners in the teaching problems they face.

To increase teacher-learner understanding of teaching and learning processes so that
they can make appropriate and informed decisions about course design and the
choice of teaching learning and assessment methods.

To foster in teacher-learners the habit of reflective teaching and professionalism in
evaluating and improving teaching.
Throughout the course, teacher-learners should be aware that their students be directed
toward obtaining:
Knowledge
Students should know:
- basic physical principles, terminology, facts, and methods
-
that physics is fundamental to many technological developments
-
that physics contributes to the social, historical, environmental, technological and
economic life of society.
TEACHER-LEARNER EXTENSION
The nature of scientific knowledge should be seamlessly integrated into all topics.
Teachers should be directed to read Scientific Knowledge found in the Extension
section of this document and available from the other lessons about science.
Understanding
Students should understand:
-
basic physical principles,
-
how to measure the quantities that are involved in the laws of physics,
-
how physical problems can be solved,
-
how scientific reasoning and concepts of evidence are key components of physics,
-
how physics relates to everyday life.
Skills
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Students should be able to:
-
measure and report physical quantities in the appropriate SI units
-
work safely in a laboratory
-
follow instructions
-
use scientific equipment appropriately
-
obtain and analyze experimental evidence.
Competence
Students should be able to:
-
present information in appropriate tabular, graphical, written and diagrammatic form
- report concisely on experimental procedures, evidence and analysis
-
use calculators
-
solve numerical problems
-
read popular science writing
-
relate scientific concepts to issues in everyday life
-
explain the science underlying familiar facts, observations, and phenomena
TEACHER-LEARNER EXTENSION
Scientific language is best learned by students if it is consistently used by the
teacher. Language forms the basis of our thinking and appropriate scientific
language is critical in communicating the nature of science. Teachers should be
directed to review nature of science language lesson available with this collection
of teacher education lessons.
Attitudes
Students should appreciate:
-
scientific attitudes are a necessary part of the nature of science
-
the contribution of physics to the social and economic development of society
-
the relationship among physics, technology, and Information Technology (IT),
-
that a knowledge of physics has many vocational applications.
TEACHER-LEARNER EXTENSION
There are also attitudes that are characteristic of scientists in their work and
different from the attitudes about or towards science listed above. These scientific
attitudes are predispositions to act and think in a scientific way. Teachers should
review the teacher education lesson on scientific attitudes—part of this series of
lessons for prospective science teachers.
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Learning
Outcomes
What any course is all about is best expressed in terms of what you will be able to do after
you complete it, assuming you do all the homework, attend all the classes, and fulfill all other
course requirements. By the end of this course, you will know how to and be able to design
and teach a course that:
- is oriented to the cognitive level and learning styles of today's traditional students
- reflects modern ideas about the nature of science and scientific reasoning
- is coherently built around assessable student-learning objectives (outcomes)
- has class-by-class assignments and activities that will directly enhance students' learning
and attainment of your learning objectives.
- motivates students to do the work assigned.
- maintains considerable discipline in your classroom.
- selects technology wisely to supplement a traditional classroom course.
- incorporates objective-focused assessment instruments.
- interprets student assessments appropriately.
By the end of the course your students should be prepared to enter the academic job market
with good, basic documentation and some job-seeking savvy. They should be able and willing
to discuss intelligently some of the major issues facing the academic world today.
A highly desirable outcome of this course is that at its end, you will have in hand the design
for your own complete course and that, given time to assemble teaching materials, implement
technologies, and deal with practical/logistical details; you would be prepared to teach that
course in a high school setting.
In more detail, the physics syllabus taken by the student will enable the
student to:
• understand the concept of certainty as expressed in significant figures/digits
• use rules for significant figures or digits to express degree of certainty
• recognise and use expressions in decimal and standard form (scientific) notations
• recognise and use prefixes indicating multiplication using exponents of 10 such as 10-12,
10-9, 10-6, 10-3, 103, 106, 109
• use an electronic calculator for addition, subtraction, multiplication and division and for
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finding arithmetic means, reciprocals, squares, square roots, sines, cosines and tangents,
exponentials, logarithms, and their inverses
• make approximate evaluations of numerical expressions and use such approximations to
check calculator calculations.
• solve simple algebraic equations
• substitute for physical quantities in physical equations using consistent units
• formulate simple algebraic equations as mathematical models of physical situations
• comprehend and use the symbols >, <, ∝, =, x, Δx.
• calculate the area of right-angled triangles, circumference and area of circles, surface
area and volume of rectangular blocks, cylinders and spheres
• use Pythagoras’ theorem, similarity of triangles, the angle sum of a triangle
• use sines, cosines and tangents in physical problems
• recall that sin θ ≈ tan θ ≈ θ/radians, and cos θ ≈ 1 for small θ
• translate between degrees and radians and ensure that the appropriate system is used.
• find the resultant of two perpendicular vectors, recognising situations where vector
addition is appropriate
• obtain expressions for components of a vector in perpendicular directions, recognising
situations where vector resolution is appropriate.
• translate information between numerical, algebraic, verbal and graphical forms
• select appropriate variables and scales for graph plotting
• determine the slope of a linear graph and allocate appropriate physical units to it
• choose by inspection a straight line that will serve as the best straight line through a set
of evidence presented graphically.
A Challenge for Prospective Teachers
Good preparation involves more than knowing topics in physics and mathematical
manipulations. If you can prove the equation for the period of a satellite in circular motion,
while blindfolded, standing on one leg, with one hand tied behind your back and whistling,
your students may be impressed by the physical dexterity involved but not necessarily by the
physics. You need to know more than the basic physics. You need to know about the nature
of science, the important role of experimentation, the people involved, the common
applications, the implications for society and popular conceptions or misconceptions. In short
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you need some background information. This is what brings the subject alive and makes it
relevant to the students’ experience.
In preparing for a student experiment or demonstration it is not enough to know the account
that is given in the textbook. It is important to test the experiment or demonstration in
advance of the class, to know the limitations of the experiment and of the apparatus, and to be
aware of the things that can go wrong and how to deal with them. Physics experiments do
work provided they have been set up properly, sources of error have been identified and
proper precautions have been taken. All of this is easier said than done. Where do you get this
background information? Textbooks tend to be fairly concise in their treatment of the course
and are written with the student, not the teacher in mind. Background information tends to be
gleaned from general reading, from magazine and newspaper articles, from television
programmes and from lectures. It is generally accumulated over many years of teaching.
TEACHER-LEARNER EXTENSION
Teachers are often too fixated on making sure that an experiment “works” in the
sense that the expected answer is always obtained. Many textbooks provide only
verification experiments. Used exclusively, this promotes a wrong picture of
science. Scientists tend not to do experiments to simply verify what they already
know; they usually do experiments to create and test concepts before using them.
See the lesson in this series titled Create Test Use.
A good pedagogic strategy is occasionally to have students put their own personal
concepts and hypotheses to the test. This is an effective means to address
misconceptions or alternate conceptions that students often have. See the lesson in
this series titled Constructivism.
It is very important in science courses that students do as much experimental work
as possible using a variety of inductive and deductive empirical problem-solving
strategies. See the lesson in this series called Empirical Problem Solving.
Readings
Books:
1. William C. Elmore and Mark A. Heald, Physics of Waves
McGraw-Hill Book Company Inc., U.S.A (1969).
2. D. Haliday, R. Resnick, and J. Walker, Fundamental of Physics, 4th Edition, John
Wiley and Sons Inc., U.S.A (1993).
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3. Frank W.K. Firk, Essential Physics, Part One, Yali Univ., (2000)
4. Raymond A. Serway, J. Madison and John W. Jewett, Physics for Science and
Engineers, 6th ed. Thomson Brooks/Cole, (2004).
Assistance Web Site:
Lesson
Plan

See Science Reasoning Text at the CRYSTAL Alberta website.

See the rest of the lessons for teacher education created for this project.

See the Alberta Education list of directing words.
In this section, teacher-learners learn how to plan, use and adapt their class lessons through
observation and by evaluating their own lesson plans. Pacing, timing, activities, and
integration of the four skills are covered. In addition, they get assistance in planning their
lessons for their practice teaching.
Their plan should effectively include, for example, these requirements:
- Planning and preparing class lessons; e.g., employing introductions and closures
- Using teaching materials effectively; e.g., blackboards, data show and overhead projectors
- Developing rapport with the students; e.g., accepting questions and soliciting answers
- Using a variety of classroom management techniques; e.g., moving around the classroom
- Using a instructional techniques; e.g., discussions, group work and laboratory work
- Analyzing and evaluating one's own teaching; e.g., creating a teaching journal
- Demonstrating techniques; e.g., through presentations and peer teaching
- Attending class, actively participating in class and completing all assignments.
TEACHER-LEARNER EXTENSION
The following information is specific to the topic of waves. Keep in mind that
regardless of the specific topic your teaching should promote scientific reasoning
including scientific attitudes, language, knowledge and problem-solving processes.
See the lessons in this series that focus on theses topics.
All students have varying degrees of preferred learning styles, multiple
intelligences, cognitive levels, prior learning, and relevant experiences. See, for
example, the CMASTE webpage on instructional emphases and the document with
Internet links at the bottom of that webpage. In general research and experience
indicates that it is very useful to use as many demonstrations and student activities
(hands-on and minds-on) as possible—to give every students a chance to succeed.
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Waves
The world is full of waves: sound waves, waves on a string, seismic waves, and electromagnetic waves, such as visible light, radio waves, television signals, and x-rays. All of
these waves have as their source a vibrating object, so we can apply the concepts of simple
harmonic motion in describing them. In the case of sound waves, the vibrations that produce
waves arise from sources such as a person’s vocal chords or a plucked guitar string. The
vibrations of electrons in an antenna produce radio or television waves, and the simple upand-down motion of a hand can produce a wave on a string. Certain concepts are common to
all waves, regardless of their nature.
Periodic motion, from masses on springs to vibrations of atoms, is one of the most important
kinds of physical behaviour. According to Hooke’s law, the force is proportional to the
displacement, tending to restore objects to some equilibrium position. A large number of
physical systems can be successfully modeled with this simple idea, including the vibrations of
strings, the swinging of a pendulum, and the propagation of waves of all kinds. All these
physical phenomena involve periodic motion. Periodic vibrations can cause disturbances that
move through a medium in the form of waves. Many kinds of waves occur in nature, such as
sound waves, water waves, seismic waves, and electromagnetic waves. These very different
physical phenomena are described by common terms and concepts introduced here.
The vibrating motions have taken place in ideal systems that oscillate indefinitely under the
action of a linear restoring force. In all real mechanical systems, forces of friction retard the
motion, so the systems don’t oscillate indefinitely. The friction reduces the mechanical energy
of the system as time passes, and the motion is said to be damped.
TEACHER-LEARNER EXTENSION
Many important empirical properties of periodic motion can be demonstrated using
a mass hanging on the end of a vertical spring. It is very useful for the topic of
waves to spend some time investigating this simple harmonic motion. You might
start by asking students to come up with qualitative and quantitative descriptions.
From their answers you can develop the concepts of oscillation (cycle), wavelength,
frequency, period, displacement, amplitude, turning points, and equilibrium
position. All of these quantities can be illustrated through animations.
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A pendulum is an excellent system for student experimentation. It requires minimal
equipment, illustrates many important aspects of simple harmonic motion, and
provides practical experience in scientific problem solving. The class can
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brainstorm possible variables that might affect the period of a pendulum. Different
groups can investigate a different variable by formulating an hypothesis and
experimental question (in terms of variables), by making a prediction, and by
designing, conducting, analyzing and evaluating their experiment.
Resonance is an interesting and important phenomenon that is easily demonstrated
with a series of pendulums. Set up several pendulums with varying lengths on a stiff
rod making sure at least two of them have the same length. Have students make
predictions and then test them. Discuss (by describing and explaining) many realworld examples involving collapse of bridges, rattles in cars, breaking wine glasses,
tuning radio stations with the support of documentary videos or animations.
What is a Wave?
When you drop a pebble into a pool of water, the disturbance produces water waves, which
move away from the point where the pebble entered the water. A leaf floating near the
disturbance moves up and down and back and forth about its original position, but doesn’t
undergo any net displacement attributable to the disturbance. This means that the water wave
(or disturbance) moves from one place to another, but the water isn’t carried with it.
When we observe a water wave, we see a rearrangement of the water’s surface. Without the
water, there wouldn’t be a wave. Similarly, a wave traveling on a string wouldn’t exist
without the string. Sound waves travel through air as a result of pressure variations from point
to point. Therefore, we can consider a wave to be the motion of a disturbance.
Mechanical waves require a source of disturbance, a medium (physical substance) that can be
disturbed and some physical connection or mechanism through which adjacent portions of the
medium can influence each other. All waves carry energy and momentum. The amount of
energy transmitted through a medium and the mechanism responsible for the transport of
energy differ from case to case. The energy carried by ocean waves during a storm, for example, is much greater than the energy carried by a sound wave generated by a single human
voice.
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TEACHER-LEARNER EXTENSION
To make the connection between periodic motion and waves, a variety of physical
models can be used—be creative. For example,
- using a slinky or similar spring with coloured pieces of paper attached to the end
coils and several widely spaced coils along the spring
- slowly pull, in a direction perpendicular to the plane of the pendulum, a wide strip
of paper from underneath a swinging pendulum that has a bucket of sand with a hole
in the bottom as the weight (the periodic motion is traced on the paper in sand)
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- slowly pull the recording paper underneath an oscillating air puck sitting on an
inclined spark table (can be pulled either perpendicular to the motion of the air puck
for transverse wave model or parallel for a longitudinal wave model)
- As a wheel (with a peg on its perimeter) turns at a constant speed, the shadow of
the peg sweeps back and forth on the surface beneath. The spot moves fastest near
the center of its sweep and slows to a stop at the end of its sweep. The center is the
spot’s equilibrium position. The movement of this spot is an example of the simple
harmonic motion.
No matter what physical model is used, be sure to discuss the relationships between
the model used and the properties discussed under periodic motion. The new
variable introduced here is the speed of the wave.
Consider the Learning Cycle when starting any topic in science. The 5E’s of the
learning cycle include engage, explore, explain, extend and evaluate. See links to
descriptions of the learning cycle by going to the lesson called Instructional
Emphases, and downloading the file at the bottom of the page. To start use, for
example, the “snowball” technique. Have each student individually write down his
or her definition of a wave. Have the students crumple the paper and then throw it
across the room to other students. After fetching all of the “snowballs”, students will
anonymously read the definitions out loud. This is a constructivist-type strategy—
to anonymously illicit alternative conceptions.
Waves and Energy
Waves transmit energy without transmitting matter. This means that waves can move energy
(or information) from one place to another without moving any substance from one place to
another. The amount of energy that a wave has depends on its amplitude. Most mechanical
waves travel through a substance (called a medium) but only move the particles in the
medium backwards and forwards (longitudinal) or move the particles from side to side
(transverse) while the wave passes. After the wave has gone, the substance is back where it
started but energy has been transmitted by the wave from its origin (where it begins) to its
destination (where it finishes).
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TEACHER-LEARNER EXTENSION
Using a slinky and other coils such as a stiffer coil, compare the motion of the
source, the individual coils (particles of the medium) and the motion of the wave
along the coil (medium). Be sure to include frequency, period, and amplitude in
your discussion. The two main types of mechanical waves—transverse and
longitudinal—can be easily introduced and demonstrated. Note that for both types
of mechanical waves, the frequency of the wave is determined by the source and the
speed of the wave is determined by the medium. This can be easily shown with long
springs of different stiffness, or with two loudspeakers having different power or
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geometry.
This is probably a good time to distinguish between an individual wave pulse and a
wave as a continuous series of wave pulses. Examples of a wave pulse are a brief
loud sound, a single ripple of water when pebble is dropped into the water and an
earthquake. The term, wave, usually refers to a continuous series of pulses such as a
constant sound of a whistle and water waves on an ocean. Simple digital cameras
and cell phone cameras can be used to freeze the image of a travelling pulse or
wave.
Remember that teacher education not only includes how but also why.
Education research and conceptualization indicates that students learn better
(qualitatively and quantitatively) if attention is paid to, for example, their cognitive
level (e.g., concrete to abstract) and their multiple intelligences (e.g., visual/special
learners). This type of why question needs to be asked constantly in teacher
education programs. See the Instructional Emphases summary at CMASTE.ca.
A General Description of Waves
Waves transmit energy without transmitting matter. Most waves move through substance but
only move it backwards and forwards (longitudinal) or side to side (transverse) while the
wave passes.
Longitudinal Waves
When a longitudinal wave moves through a material, the particles of the material move
backwards and forwards along the direction in which the wave is travelling.
Below is a picture of a longitudinal wave travelling along a spring.
Rarefaction is the name given to the region where the coils of the spring are pulled apart.
Compression is the name given to the region where the coils of the spring are pushed
together. Wavelength can be measured as the distance between the centres of two
compressions. Sound waves and P waves from earthquakes are examples of longitudinal
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waves.
TEACHER-LEARNER EXTENSION
Once students have seen and experimented with longitudinal waves on a slinky, ask
them to qualitatively sketch a graph of density of the coils on the y-axis versus the
density of the coils along the x-axis. The sine curve obtained is a mathematical
representation of a longitudinal wave (not a visual representation as shown in the
diagram above). This will help students to understand that we often use the sine
curve to represent any type of wave whether it is longitudinal in nature or
transverse. Discuss the need for teachers and students to understand the difference
between concrete observation and abstract thinking in science (including abstract
conventions of communication that are seemingly unrelated to reality).
Transverse Waves
All of the waves you will meet in your course are transverse except sound waves and P waves
from earthquakes. When a transverse wave travels through a substance the particles of the
substance are moved at right angles to the direction in which the wave is traveling. The
particles either moves up and down or from side to side as the wave goes past (like waves on
the surface of the sea). After the wave has gone, the particles are back where they started.
Below is a representation of a transverse wave.
Amplitude can be defined as the maximum displacement from the average or equilibrium
position. The amplitude of the wave is measured from the peak (also known as crest) or
trough to the mid-point or equilibrium position. Amplitude is a measure of how much energy
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the wave has.
Wavelength, , can be defined as the distance the wave has traveled during one complete
cycle and is typically measured between two successive crests or troughs. Because
wavelength is a distance, it is measured in metres. The period, T, of a wave is the time in
seconds required for one complete cycle of a wave. For a wave travelling at a constant speed,
v 
d
t


T
However, it is customary to use frequency instead of period to describe both the source and
the wave produced by the source. Frequency, f, is defined as the number of complete cycles
(complete waves) in one second and is the inverse of the period. One unit of frequency or one
cycle per second is defined as a Hertz, symbol Hz. Rewriting the mathematical equation for
the speed of a wave,
v 

T
1
  
T 

f
The final expression, v = f , is known as the universal wave equation. Note that the speed of
a mechanical wave is completely determined by the medium and the frequency of the wave is
completely determined by the source.
TEACHER-LEARNER EXTENSION
The derivation of the universal wave equation should be followed by a unit analysis
by the students so that they will see that the both sides of the equation have identical
units. This would also be an appropriate time to practice some mathematical
problems using various examples of both longitudinal (e.g., sound) and transverse
(e.g., water) waves. Use contexts familiar to students to assist in meeting the
outcome of relating physics to the world around them.
If you have a slinky and other long coils available, this is another opportunity to use
them to reinforce the various descriptions and properties of mechanical waves,
especially related to the universal wave equation. You might also pose the
questions: What variable determines the initial amplitude of a wave? What happens
to the amplitude as the wave travels out from the source? What property of the wave
classifies the wave as being either longitudinal or transverse?
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Periodically a teacher needs to take the opportunity to reinforce international
conventions of communication used in the scientific community; e.g., SI and
IUPAC. For example, equations that represent phenomena use international quantity
symbols such as velocity (v), frequency (f) and wavelength () as in v = f . The
quantity symbols are to be in italics, whereas unit symbols are not to be in italics;
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e.g., 2.0 mm and 2/s, and 14 m/s). Based on international rules of communication
using an x in an equation is wrong—x is a variable like any other symbol in an
equation, not multiplication sign. Teachers need to learn the importance of
following conventions of communication and then decide to what extent their
students should learn and use these rules.
Common Waves
Sound Waves
Sound is a longitudinal wave that can travel through gases (such as air), liquids (such as under
water) or solids (such as the Earth). Sound cannot travel through a vacuum. The speed of a
sound wave depends on the density of the medium (substance) through which it is travelling.
The more dense the medium, the faster the sound wave will travel. Sound will travel faster
through the Earth than under water, and faster under water than it will in air. The speed of
sound in air is approximately 330 m/s.
TEACHER-LEARNER EXTENSION
A simple model for density and speed of sound is a row of dominoes standing on
end. When the dominoes are relatively far apart and the first domino is tipped, the
collisions along the row proceed more slowly than if the dominoes are standing
much closer together. This simple physical model relates to collisions between
particles in the medium and the speed of transfer of these collisions throughout the
medium.
Teachers should learn about models (including analogies and metaphors) and
make their use explicit to students. There are many kinds of models (including
physical and abstract) used to communicate natural and technological phenomena.
Scientists and science teachers make extensive use of models to make the abstract
more concrete to students. Research suggests that students do not simply move from
a cognitive level of concrete operational to formal operational by growing older—
they grow in cognitive level through experience and learning. It is being suggested
here that teachers should use every opportunity to help students grow from one
cognitive level to the next by using models as often as possible.
Most people can hear sounds with frequencies between 20 Hz and 20 kHz. Sounds with a
frequency higher than 20 kHz are called ultrasound and are used in a variety of situations
such as range finding, scanning and cleaning. Sound waves can be reflected (called an echo),
refracted or diffracted.
TEACHER-LEARNER EXTENSION
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To demonstrate that the source of sound waves is a vibrating object, strike a tuning
fork and touch the tip of the tuning fork into the surface of water. Vibrating strings
such as on a guitar also show the blurred motion of the string as the source of the
sound.
What is the source of sound for the human voice? How does a human make
different sounds (different frequencies)? Musical instruments also provide many
good examples. Discuss the source of the sound in brass, reed and string
instruments. If possible, have students bring or play some musical instruments to
provide an interesting context for a discussion of sound waves.
Dropping several sticks of different materials onto the floor yields different sounds.
Use this evidence as an object of discussion for the students.
Discuss why a teacher would want to supplement the direct teaching of the physics
of optics with the above activities. Refer to the Instructional Emphases document at
for assistance in answering this question.
The loudness of sound depends on the amplitude of the wave. The greater the amplitude, the
louder is the sound. The pitch of sound (how high the note is) depends on the frequency of the
wave. The higher the frequency, the higher the pitch. Below is a representation of a sound
wave that has been changed into alternating current by a microphone and displayed on a
cathode ray oscilloscope (CRO).
If the sound is made louder and with a higher pitch, the shape of the wave changes as shown
below. The resulting curve has a greater amplitude (louder) and more cycles per second
(higher frequency or pitch).
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TEACHER-LEARNER EXTENSION
This is a good opportunity to have your students draw a variety of waves showing
amplitude and frequency—based on the studied wave equations. Students should be
able to draw waves that have the same amplitude but different frequency or the
same frequency and different amplitude. They should also be able to describe the
sounds associated with their diagrams. Graph paper may make it easier for students
to carefully draw different waves and lead to a qualitative comparison. If they were
to draw their waves on a large-scale format such as a black board they could
describe the differences to the rest of the class. This method of teaching and
learning amongst peers is a powerful technique to reinforce concepts.
There are many relatively simple student activities that can be done with sound
waves. For example, comparing the sound of different tuning forks and rubbing a
wet finger on the edge of a wine glass. Students can replicate a phonograph by
making a large paper cone with a straight pin in the small end of the cone,
perpendicular to the axis of the cone. Holding the cone so that the pointed end of the
pin rests lightly in the groove of a vinyl record can reproduce the recorded sound
(some experimentation with different pins and cone sizes may be necessary). If you
discussed resonance previously, hold a tuning fork above a hollow tube whose
bottom end is immersed in a cylinder of water. Strike the tuning fork and then raise
or lower the hollow tube. At a certain length of the air column in the hollow tube, a
loud (resonant) sound is produced.
Again, this is the how for creating deeper understanding and promoting inquiry.
Remember to also discuss the why; e.g., catering to different learning styles and
multiple intelligences, and using an inquiry-based learning cycle.
Water Waves
Naturally occurring waves on the surface of water are usually wind-generated waves.
Transverse waves travel on the water surface and these are the waves which we see as they
make the surface go up and down. Transverse water waves are typically represented by as a
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series of parallel lines. These lines represent the crests (peaks) of the wave, if you are looking
down on them from above.
Longitudinal waves can travel through water underneath the surface. This is underwater
sound and can be used by sea creatures to communicate (whales, dolphins etc.) and by boats
for echo location.
TEACHER-LEARNER EXTENSION
This is a good opportunity to introduce the ripple tank and have students do some
initial experimentation. Wave pulses can be generated either by a point source (e.g.,
a pencil) or a straight wood rod (with a diameter greater than the depth of water).
Show that the medium does not move by placing a small piece of cork (or similar
floating object) and observing the effect as the wave passes. A mechanical wave
generator or simply rolling a wood rod back and forth can be used to generate a
wave whose appearance when illuminated from above is similar to the diagram
above. (A ripple tank can also be placed on the stage of an overhead projector.)
Relate observations made to speed, wavelength and frequency of the wave. Videos
showing the ocean water motion during ebb and flow will be beneficiary.
The relationship among speed, wavelength and frequency can be created
(inductively create a hypothesis such as ), tested or used
Earthquake Waves
Earthquakes produce waves called seismic waves (pronounced "size-mick waves"). These
waves are measured by an instrument called a seismograph or seismometer. There are two
main types of seismic waves: body waves and surface waves. Body waves move within the
Earth and are identified as P waves (longitudinal) and S waves (transverse) and provide
valuable information about the inside of our planet. Surface waves are primarily transverse
and can cause vertical or horizontal movements of the surface.
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TEACHER-LEARNER EXTENSION
Earthquakes occur frequently in many parts of the world and these are sometimes
associated with tsunami waves. Use stories in the media to relate to waves and
sources of waves. In particular, how is a tsunami wave similar and different from an
ordinary water wave? How can you simulate an earthquake and resulting tsunami in
a ripple tank? Why would you like to simulate an earthquake wave? Is it possible
that some animals perceive earthquake waves before the the earthquake is felt?
Provide your reasoning?
Light Waves
All of the common waves discussed above are mechanical waves that require a physical
medium. Electromagnetic waves are transverse waves that do not need a medium or substance
to travel through. Light is the most familiar example of an electromagnetic wave and is
therefore a transverse wave. Visible light is one very small part (region) of the
electromagnetic spectrum. Light is the visible region and is the part our eyes are able to see.
Like any electromagnetic wave, light can travel through a vacuum such as through the
vacuum of space from the Sun to the Earth. Light travels very quickly. The speed of light is
approximately 3.0 x 108 m/s in air (three hundred million metres per second) There is nothing
which can travel faster than light.
The speed of sound in air is approximately 330 m/s, so light is almost one million times as
fast. You can sometimes notice that light is traveling faster than sound. If you watch a cricket
match you can see the batsman hit the ball before you hear the sound. The light has traveled
to your eyes more quickly than the sound has traveled to your ears.
TEACHER-LEARNER EXTENSION
A ray box or an inexpensive laser pointer is useful to obtain a thin ray of light. This
can be used to illustrate many properties of light. Unlike most mechanical waves,
the wavelength of light (electromagnetic radiation) is much too small to see. Why
do we hypothesize that light is a wave? What evidence do we have (for and/or
against) your hypothesis?
As a natural phenomenon, a thunderstorm can be shown to illustrate many
properties of light waves, as well as the physical difference between the light waves
and sound waves.
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Properties of Waves
All waves—mechanical or electromagnetic, longitudinal and traverse—exhibit properties
such as reflection, refraction, diffraction and interference. There are other properties such as
polarization that apply only to transverse waves.
TEACHER-LEARNER EXTENSION
An introduction to some properties of waves is best done starting with onedimensional waves on a spring. For example, have students explore:
- reflection of a wave pulse in a slinky using both fixed and loose ends.
- wave pulses on a slinky attached to another stiffer spring or to a piece of string.
This also introduces the concept of a boundary while showing both reflected waves
and transmitted waves.
- what happens when two waves meet? This is a good introduction to the principle
of superposition and the property of interference.
Although this is only a one-dimensional system, many important properties of
waves can be explored by the students. Be sure to question students about speed,
frequency and wavelength changes. Test and/or use the wave equation
hypothesis. Test and/or use the learning styles and multiple intelligences
hypothesis—view every science-education lesson as education research.
Reflection
Any type of wave can be reflected at a boundary. After reflection, a wave has the same speed,
frequency and wavelength; it is the direction of the wave that has changed. The echo of a
sound is an example of reflection.
Water waves are reflected from a solid, plane boundary as shown below.
Note that the total length of the line representing the wave peak stays the same where it is
being reflected. The red part of the incident wave plus the blue part of the reflected wave is
the same as the original line. After reflection, a wave has the same speed, frequency and
wavelength, it is only the direction of the wave that has changed.
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TEACHER-LEARNER EXTENSION
Use a ripple tank to demonstrate reflection of water waves. Start with a single,
straight wave pulse (by moving a wood rod slightly) that travels toward a solid,
smooth plane barrier sticking out of the water. It is important to establish some
conventions and terminology; e.g., plane, incident, reflected, wave ray, normal.
Use a variety of angles and ask students to make observations and create a
generalization about reflection. Test this generalization using incident straight
wave pulses with a curved boundary and incident circular wave pulses using a
straight barrier. (This generalization has been well established and accepted by the
scientific community and becomes the law of reflection.) Some students may want
to explore circular waves striking a curved barrier.
Use an electric motor straight-wave generator (or manually rocking a wooden rod
back and forth) to generate continuous incident and reflected waves as shown in the
diagram above. This is useful to establish that the wavelength and speed do not
change upon reflection. Note that the frequency is fixed by the constant source.
Note the inquiry-based learning that is being promoted by these suggestions. Also
note that the emphasis on empirical scientific work reinforces the pedagogic
hypothesis of starting with the concrete and moving to the abstract. Research
shows that this is the way that scientists have learned about the natural world and
similar research shows that this is the way that students learn best.
Light is also reflected by many surfaces such as a mirror. A flat shiny surface, like a plane
mirror, is a good reflector of light. A plane mirror is one that is straight and not curved.
The light ray that hits the mirror is called the incident ray. The light ray that bounces off the
mirror is called the reflected ray. According to the law of reflection, the angle of incidence
equals the angle of reflection, i = r. Note that both angles are measured from an imaginary
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line, called the normal, that is perpendicular to the reflecting surface. If the surface of the
mirror is not smooth (rough or bumpy), then light will be reflected at many different angles.
The image in the mirror will be blurred and unclear. This is called a diffuse reflection.
TEACHER-LEARNER EXTENSION
Use a ray box or a laser pointer, a piece of paper and a small, rectangular plane
mirror to demonstrate reflection of light. This is best arranged by having the
incident light shining just along the surface of the paper to make the light visible.
Angles can easily be measured, especially if circular graph paper is used.
Challenge students to predict the angles of two mirrors required to simulate a
periscope. This can then easily be tested. Prediction is the most severe test that a
concept can be put to. Predictions are based upon a testable hypothesis.
Pedagogic experience indicates that students who are actively engaged in their
learning are more likely to retain what they have learned and to be able to transfer
what they have learned.
When you look into a mirror, you see a reflection that is an image of the real object.
The image appears to be the same distance behind the mirror as the real object is in front of it.
This is because the brain thinks that light travels in straight lines without changing direction.
The image is called virtual because it does not really exist behind the mirror. The virtual
image is the same size as the object but with left and right reversed.
Refraction
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Refraction is the change in direction of a wave at the boundary between two different media.
Any type of wave can be refracted. Refraction occurs because the speed of a wave changes, as
it moves at a non-zero angle of incidence from one medium to another. After refraction, the
wave has the same frequency but a different speed, wavelength and direction.
Water waves travel faster on the surface of deep water than they do on shallow water. The
change in speed of the wave will cause refraction.
As you can see, the change in speed has changed the direction of the wave. The slower wave
in the shallow water has a smaller wavelength. The amount of refraction increases as the
change in speed increases.
TEACHER-LEARNER EXTENSION
Refraction of water waves can be easily modelled by placing a glass plate on the
bottom of a ripple tank with one edge of the plate at an angle to the incident wave.
This creates a deeper water region and a shallower water region in the tank. For
water waves in relatively shallow water, the speed of the waves depends on the
depth. The pattern of water waves illuminated by a light from above, can be
photographed for analysis. Use your digital camera for gathering evidence.
Using either a photograph or a carefully drawn diagram, label the normal, angle of
incidence and angle of refraction. This establishes quantitatively that the direction of
the waves is changed. Using the universal wave equation, the fact that the source is
constant (and therefore the frequency does not change) and some trigonometry of
right-angle triangles, the sine law of refraction can be determined.
v1
1
sin 1


v2
2
sin  2
Notice that there are two requirements for refraction, the speed (or medium) must
change and the angle of incidence must be non-zero.
With some additional experimentation, students can show that the waves bend
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towards the normal when it enters a medium where the speed is lower, and bends
away from the normal when the waves enter a medium where the speed is greater.
Notice that you are meeting three categories of goals for science education:
learning some pure-science knowledge, learning about the nature of science and of
scientific knowledge, and learning how to learn/teach.
Refraction of Light
A material is transparent if you can see through it. If you can see through it, it means that
light can travel through it. Transparent materials include air, glass, Perspex, and water.
Light travels at different speeds in different materials because they have different densities.
The higher the density, the slower light travels. Light travels fastest in space (a vacuum) and a
little slower in air. Light moves noticeably more slowly in glass than in air because glass is
obviously denser. A line drawn at right angles to the boundary between the two media (air
and glass) is called a normal.
Light which enters a glass block along a normal does not change direction but it does travel
more slowly through the glass and so its wavelength is smaller. Technically, this is not
refraction because there is no change in direction of the light ray.
However, when a ray of light enters a glass block at a non-zero angle of incidence it changes
speed, wavelength and direction as shown below.
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In going from a less dense medium (air) to a denser medium (glass) light bends towards the
normal. This means that i > r (the angle i is greater than the angle r). In going from a more
dense to a less dense medium (glass to air), light bends away from the normal.
TEACHER-LEARNER EXTENSION
A slightly cloudy (“smokey”) glass or plastic will show the light ray inside the new
medium. Otherwise, to show this bending you will need to shine a light ray along a
paper surface with the block of glass or plastic sitting on the paper.
There are many simple examples of refraction.
With a clean block glass and several short steel needles or pins students can make
the arrangement shown in the above figure. For different incident angles they can
determine the corresponding refracted angle by viewing the fixed incident needles
from the other side through the glass.
An object such as a pencil sitting in a transparent glass half-filled with water is one
example. Have students carefully observe this and relate this to the bending of light.
Another demonstration uses an opaque cup with a coin in the centre of the bottom
(or a black dot drawn on the bottom). Set the cup on a table and have the students
move away until the coin or dot just disappears from view. Without moving the cup
or your position, have someone slowly add water to the cup. Ask students to draw a
ray diagram to explain their observations.
Mirages are a natural example of the refraction of light. Eye glasses, binoculars,
some telescopes and fibre optic cables are a technological examples dependent on
the refraction of light. Open a discussion on the relationship between science and
technology. Some say that science leads/creates technology, while others say that
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technology leads science and that science is only useful to explain a technology that
has already been invented. What is your view—with historical examples?
Refraction and Colour
Water droplets in the sky (creating a rainbow) or transparent objects can refract light and
separate the white light into its component colours. A glass prism of angle 60o disperses white
light into its different colors and create a spectrum of colours. The seven colors of light are
red, orange, yellow, green, blue, indigo and violet. You can remember the colors and order by
remembering “Richard of York gave battle in vain” or by noting the letters ROYGBIV.
Each color of light has a slightly different frequency and wavelength. Therefore, the different
colors are refracted at slightly different angles. Red light has the longest wavelength and is
refracted least. Violet light has the shortest wavelength and is refracted most.
A most charming example of chromatic dispersion is a rainbow. When white sunlight is
intercepted by a falling raindrop, some of the light refracts through the drop, reflects from the
drop’s back, inner surface, and then refracts out of the front of the drop. As with the prism,
the first refraction separates the sunlight into its component colors, and the second refraction
increases the separation. You must be positioned between the sun and the raindrops in order
to see the rainbow. Ask teacher-learners to discuss the value of a visual-models to
accompany word-explanations. Ask teacher-learners to create a demonstration of a rainbow
for a classroom; e.g., using a bright light and a mist. (In this case does the generalization hold
that the observer must be between the light source and the water drops?)
Diffraction
Diffraction is a unique wave property that does not apply to particles. For example, if a
stream of particles hits a barrier containing an opening, the particles that enter the opening
travel straight through forming a well-defined beam of particles. On the other hand, when
waves strike a barrier containing an opening, the portion of the wave that goes through the
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opening can spread out forming curved waves. Diffraction is the spreading of waves around
the edge of a barrier whether that is an opening in a solid barrier or an obstacle in its path.
Diffraction is most obvious when the wavelength of a wave is of a similar size or greater than
the size of an obstacle or an opening in a barrier. After diffraction, a wave has the same
speed, frequency and wavelength.
TEACHER-LEARNER EXTENSION
A good illustration of the diffraction of sound waves is to have students stand
outside of a building along an outer wall but not in front of a door opening. Sounds
from inside the building can easily be heard coming from an open doorway even
though the students are not directly in line with the source of the sound. The sound
waves diffract as they pass through the opening of the doorway.
Students can be assigned some calculations using the universal wave equation to
determine the wavelengths of various sound frequencies. The answers can be
compared with the typical width of a door opening. Can the wave make it through
the door? If so, will the wave be diffracted? Which frequencies diffract more?
Walls are often placed as sound barriers between highways and homes—and yet
some traffic sound does get to the homes. Ask your student how the sound arrives
their—by reflection, refraction and/or diffraction? Ask students to defend their
answers. Use this as an example of a relevant, motivational question that may
create an interactive discussion. Alternately, use this question on an exam.
Water waves can diffract when passing through a gap in a harbour wall or around the edge of
an obstacle such as a large rock or peninsula. The wavelength of water waves may be several
metres. If the wavelength is of a similar size to a gap in a harbour wall, then the wave will
diffract as shown below.
If the wavelength is much smaller than the size of the gap, then only a little diffraction will
occur at the edge of the wave.
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The part of the wave which hits the wall in the above two pictures is reflected straight back on
itself.
TEACHER-LEARNER EXTENSION
Diffraction of water waves is easy to demonstrate in a ripple tank. Use barriers with
different sized openings, a single barrier or any other solid object. Ask students to
qualitatively determine the relationship between the amount of diffraction (as
observed by the curvature of the waves) and the size of the wavelength () and also
with the size of the opening (d).
There are many excellent photos on the Internet of water waves diffracting near
coastlines. When are you seeing diffraction and when refraction?
Light waves also diffract, but because their wavelengths are very small (hundreds of
nanometres), little diffraction is usually observed with ordinary objects. To observe any
diffraction effects, very small objects or openings and careful observations are required. The
small wavelength of light means that the spreading light waves overlap and create
interference effects.
TEACHER-LEARNER EXTENSION
Diffraction and interference of light can be shown using a straight filament light
bulb as the light source. Have students look at the light source through a very
narrow slit formed by two fingers held close together. Alternatively, you can make
single and double slits by scratching with one or a pair of razor blades on a
microscope slide painted with liquid graphite (or similar coating).
CDs and DVDs illuminated with sunlight or a bright light source also show
diffraction/interference effects. The fine rulings, each 0.5 μm wide, on the compact
disc (CD) function as a diffraction grating. The diffracted light forms coloured lines
that are the composite of the diffraction patterns from the rulings on the CD.
A street light shining through a sheer curtain will often provide black diffraction
lines. Why is the diffraction pattern through the curtain only a black and white
pattern and not a coloured spectrum? How can coloured spectral lines be separated
further?
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Electromagnetic Waves
Empirically it can be shown that light behaves as a wave of very short wavelengths. Because
light does not require a physical medium like mechanical waves, the nature of light has been
the subject of considerable debate in the scientific community for centuries. According to
Maxwell’s theory, developed in the 1860s, transverse waves of mutually perpendicular
electric and magnetic fields are produced from oscillating electric charges. These
electromagnetic waves travel out from the source at the speed of light and can travel in a
vacuum like sunlight from the Sun to the Earth. They can have a wide variety of wavelengths
and frequencies that form the electromagnetic spectrum.
Electromagnetic waves can have wavelengths that range from several thousand metres for
radio waves to less than picometre (1012 m) for gamma rays. The following diagram (not to
scale) represents the main regions of the electromagnetic spectrum.
Radio
Microwave
Infrared Visible
Ultraviolet
Gamma
ray
X-ray
TEACHER-LEARNER EXTENSION
Assign different regions of the electromagnetic spectrum to different students (or
small groups) and ask them to prepare and present a report to the class for their
region. Their report should include a typical source of the electromagnetic waves,
the range of wavelengths and frequencies, a typical object that could be detected by
these waves, some applications and safety hazards, if any.
Alternately, create “home” groups the day before for some group (cooperataive
learning) work the next day. Assign each student of a “home” group to become an
expert on one of 4-7 regions of the electromagnetic spectrum (depending on the
number of students). Next day place all of these experts at one table to discuss/share
their findings/expertise for approximately 10 min. Then send the experts back to
their “home” group to, in turn, teach their group about the region of the
electromagnetic spectrum for which they have expertise.
Radio Waves
Radio waves are used for broadcasting radio and TV programmes. The transmitted
information may be analogue or digital and uses a radio wave as a carrier. Very long
wavelength radio waves can travel around the Earth despite its curvature, diffracting around
the Earth's surface. These are sometimes called ground waves. Medium wavelength radio
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waves are reflected from an electrically charged region of the Earth's atmosphere called the
ionosphere. These waves are sometimes called sky waves and can also be sent from one part
of the Earth to another. Shorter wavelength radio waves pass straight through the atmosphere
and cannot be used to send information around the Earth's curvature. These waves are
sometimes called space waves and can be used to send information in a straight line across
the Earth's surface.
Microwaves
Microwaves have wavelengths shorter than radio waves. Some of these wavelengths pass
easily through the atmosphere and are used to transmit information to satellites. Mobile phone
networks use microwaves. Other microwaves have wavelengths that are absorbed by water
molecules. Microwave cookers use these waves to transfer energy to the water molecules in
food, causing it to get hot. Living cells can also absorb microwaves. The cells may be
damaged or killed by the heating effect of the waves.
Infrared (IR)
Infrared waves (often called infrared radiation) are easily absorbed by materials. The energy
of the wave causes the material to get hot. We usually think of infrared radiation as heat.
Ordinary ovens, grills and toasters use infrared radiation to cook food (ovens may also cook
by convection). Infrared waves can transmit information through the air to operate TV's and
VCR's by remote control. (Infrared radiation can sometimes be seen by looking at a remote
control device through a cell phone camera or digital camera.) Information can also be sent
through optical fibres. Intense infrared radiation will damage or kill living cells (such as skin
cells) by burning them.
Ultraviolet (UV)
Ultraviolet waves are often called ultraviolet light or ultraviolet radiation. Some materials will
absorb the energy from ultraviolet waves and emit (give out) the energy as visible light. These
materials are called fluorescent and are used for fluorescent lighting. (sometimes called strip
lighting) and security marking. Ultraviolet light from the Sun causes skin to tan. Sun tanning
beds emit ultraviolet light to give an artificial tan. Intense ultraviolet light in strong sunlight
can damage cells deep inside skin tissue. This type of damage can result in skin cancer.
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Darker skin is more resistant to ultraviolet light than lighter skin. To be safe, avoid strong
sunlight or use a skin sun-block (see sunscreens). Ultraviolet light can be used to start
chemical reactions. This is sometimes used in dentistry to fuse repairs. Very intense
ultraviolet light will kill living cells, including some forms of bacteria. This is sometimes
used to sterilize objects.
X-rays
Electromagnetic waves with a wavelength shorter than ultraviolet light are called X-rays (not
X waves). X-rays can pass easily through flesh but not through bone. X-ray photographs
show the image of bones against a black background. These photographs can show if bones
are broken or damaged. X-ray diffraction can give information about the arrangement of
atoms in materials. Low intensity X-rays can damage living cells and cause cancer. People
who work with X-rays take measures to protect themselves from exposure. They wear a film
badge and stand behind special screens when the X-ray machine is switched on. High
intensity X-rays will kill living cells.
Gamma rays
Electromagnetic waves with a wavelength shorter than X-rays are called gamma rays or
gamma radiation (not gamma waves). Gamma rays may be emitted from radioactive
materials. Low intensity gamma radiation can damage living cells and cause cancer. High
intensity gamma radiation will kill cells. It is used in a technique called radiotherapy to treat
cancer by targeting the cancer cells with a beam of radiation and then rotating the source of
the beam as shown below.
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The normal cells receive a lower dose
of gamma radiation than the cancer
cells, where all the rays meet.
Radiotherapy aims to kill the cancer
cells while doing as little damage as
possible to healthy normal cells.
Gamma radiation is also used to kill
micro-organisms. It is used to sterilise
food and hospital equipment such as
surgical instruments.
TEACHER-LEARNER EXTENSION
Here is another opportunity to discuss the importance of scientific research to the
benefit of technological advances and to the benefit of individuals and society, in
general. Without the funding of basic scientific research (e.g., at universities),
technologies and the quality and length of our lives are not likely to improve.
Transmission of Electromagnetic Signals
Different types of electromagnetic waves are used for transmission, including radio waves,
microwaves, infrared and visible light. Information can be sent in the form of analogue or
digital signals.
Analogue Signals
Information in the form of speech or music can be transmitted as an analogue or digital
signal. An analogue signal will resemble the original speech or music by having the
frequency or amplitude of the wave go up and down in the same way as the sound in speech
or music goes up and down. The word analogue means "similar" or "corresponding".
Information in the form of an analogue signal can be added to another electromagnetic wave
that is used for transmission. This wave carries the analogue signal and is called the carrier
wave. For much of the last century information was transmitted in the form of analogue
signals. Today information is being increasingly transmitted using digital signals. Digital
signals have advantages over analogue signals.
Digital Signals
Information can be transmitted in the form of a digital signal. Unlike an analogue signal, the
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digital signal uses a code with two states that are called on and off. The “on” state is a small
pulse of the electromagnetic wave. The “off” state is the gap in between the pulses where
there is no electromagnetic wave. A digital signal is represented by the diagram below.
When the digital signal reaches its destination, the series of on and off states must be changed
back into the original information. This process is called decoding.
Information today is being increasingly transmitted using digital signals. Digital signals have
advantages over analogue signals such as increased capacity and better quality. Increased
capacity means that more information can be sent by digital signals than analogue signals in
the same time, using the same optical fibre or carrier wave. Digital Signals have a higher
quality than Analogue Signals. The quality of a signal is a measure of how much the signal
has changed during transmission. A high quality signal has changed very little. A low quality
signal has other information in it that was not there in the original. The additional unwanted
information is called noise. Any noise present in an analogue signal reaches the receiver and
is processed by the electrical equipment as if it were part of the original signal. All signals
become weaker as they travel and some frequencies in an analogue signal may weaken more
quickly than others. If the signal is amplified during transmission, then the noise is also
amplified in the same way. A digital signal has only two states called on and off. Since noise
is usually of low intensity compared to the signal, noise is interpreted by the decoder as an off
state and is not included in the signal processing. A digital signal ignores the noise and
therefore has a higher quality than an analogue signal.
The following Conceptual questions are presented as examples:
Samples of Conceptual Questions:
1.
If one end of a heavy rope is attached to one end of a light rope, the speed of a wave
will change as the wave goes from the heavy rope to the light one. Will the speed
increase or decrease? What happens to the frequency? To the wavelength?
2.
If an object-spring system is hung vertically and set into oscillation, why does the
motion eventually stop?
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3.
If a grandfather clock were running slow, how could we adjust the length of the
pendulum to correct the time?
4.
A grandfather clock depends on the period of a pendulum to keep correct time.
Suppose such a clock is calibrated correctly and then the temperature of the room in
which it resides increases. Does the clock run slow, fast, or correctly? [Hint: A
material expands when its temperature increases.]
5.
Why does a vibrating guitar string sound louder when placed on the instrument than it
would if allowed to vibrate in the air while off the instrument?
6.
When light (or other electromagnetic radiation) travels across a given region, what is
it that oscillates? What is it that is transported?
7.
If the fundamental source of a sound wave is a vibrating object, what is the
fundamental source of an electromagnetic wave?
Summary
(Science
Waves
In a transverse wave the particles of the medium move in a direction perpendicular to the
direction of the wave. An example is a surface water wave.
Pedagogy
Philosophy)
In a longitudinal wave the particles of the medium move parallel to the direction of the wave
velocity. An example is a sound wave.
Universal Wave Equation
The relationship of the speed, wavelength, and frequency of a wave is
v=f
This relationship holds for a wide variety of different waves.
Interference of Waves
The superposition principle states that if two or more traveling waves are moving through a
medium, the resultant wave is found by adding the individual waves together point by point.
When waves meet crest to crest and trough to trough, they undergo constructive interference.
When crest meets trough, the waves undergo destructive interference.
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Beats
The phenomenon of beats is an interference effect that occurs when two waves with
slightly different frequencies combine at a fixed point in space. For sound waves, the intensity of the resultant sound changes periodically with time
Characteristics of Sound Waves
Sound waves are longitudinal waves. Audible waves are sound waves with frequencies
between 20 Hz and 20 kHz. Infrasonic waves have frequencies below the audible range,
and ultrasonic waves have frequencies above the audible range
Standing Waves
Standing waves are formed when two waves having the same frequency, amplitude, and
wavelength travel in opposite directions through a medium.
Forced Vibrations and Resonance
A system capable of oscillating is said to be in resonance with some driving force
whenever the frequency of the driving force matches one of the natural frequencies of
the system. When the system is resonating, it oscillates with maximum amplitude.
Electromagnetic Waves and their Properties
Electromagnetic waves were predicted by James Clerk Maxwell and experimentally
confirmed by Heinrich Hertz. These waves are created by accelerating electric charges, and
have the following properties:
- Electromagnetic waves are transverse waves, because the electric and magnetic fields are
perpendicular to the direction of propagation of the waves.
- Electromagnetic waves travel at the speed of light.
- Electromagnetic waves carry energy as they travel through space
The electromagnetic spectrum includes waves covering a broad range of frequencies and
wavelengths. These waves have a variety of applications and characteristics, depending on
their frequencies or wavelengths.
Reflection
This section focuses on how the teacher learner will teach the topic according to the lesson
plan. Here they will be expected to guide their class by giving clear directions, using various
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techniques, challenging teaching scenarios and different learning styles, and present new
material interactively. As well they should be able to demonstrate how to evaluate, adapt and
create classroom resources.
TEACHER-LEARNER EXTENSION
Reflection and self-evaluation are important processes for all teachers to
continuously improve their teaching. This includes not only classroom procedures
but also the presentation of the content of teacher education. For example, the
concept of curriculum emphases (e.g., nature of science, the interaction of
science and technology, and society and environment issues) is very useful to
meet the many varied goals of modern science education. The idea here is that each
pure-science unit also employ a curriculum emphasis like described above. This
way the other goals for science education are also being met. See the teachereducation lesson on curriculum emphases.
In order to further bring the subject to the student’s mind the teacher always should be able to
discuss any applications and societal issues, relevant to the given topic. Where possible,
animations should be presented through each steps of the lecture presentation. Animations
and flashes presented in the Extension section will be useful.
Science education in the senior cycle should reflect the changing needs of students and the
growing significance of science for strategic development. Leaving Certificate science
syllabuses are designed to incorporate the following science, technology. society and
environment (STSE) components:
• Science for the enquiring mind, or pure science, to include the principles, procedures and
concepts of the subject as well as its cultural and historical aspects
• Science for action, or the applications of science and its interface with technology
• Science concerned with societal issues – political, social and economic – of concern to
citizens
• Science concerned with environmental issues—with our natural surroundings.
The four components should be integrated within each science syllabus, with the first
component having, for example, a 70% weighting. The remaining 30% should be allocated to
the other two components in, for example, the ratio 2 to 1 to 1. The syllabuses, which are
offered at two levels, Higher and Ordinary, will have approximately 180 h of class contact
time over a two-year period. They should be practically and experimentally based.
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TEACHER-LEARNER EXTENSION
Remember that there are three basic sets of goals for teacher education:
1. Pedagogic concepts, skills and attitudes based upon research and experience
in the classroom. (See, for example, the PowerPoint at the bottom of the
Teacher Education webpage and the lessons on Constructivism and on
Lesson Planning.)
2. Scientific concepts. skills and attitudes based upon research and experience
in the laboratory and in the natural environment. (See, for example, this
teacher educations lesson on the physics of optics.)
3. Nature of science, science & technology interaction, and society &
environment concepts, skills and attitudes based upon research and
experience in the laboratory, in society, and in the environment. (See, for
example, the teacher education lessons on Create-Test-Use, on Laboratory
Research Reports, and on Scientific Attitudes.
Extension
Extension should include learning more about, for example, pedagogy, science and nature of
science. There is more to learn than there is time in a life-time. Teachers need to learn from
the formal research of the university educators and from the informal research conducted by
classroom teachers. The best teachers are learners. They need to learn from those who have
come before them and to continue the inquiry of teaching on into their future. Much has been
achieved in science education but there is much more to be learned. Teacher education is
kinetic, not static. Each teacher needs to become an expert on some aspect of teaching and
learning and to share their expertise in a collaborative way with other teachers and learners.
Teacher education is a research and development discipline—creating, testing and then using
pedagogic concepts. Every time a teacher walks into a classroom research and development is
occurring. Taking conscious control of this research and development is the responsibility of
every science teacher.
Websites to Explore
Through the following online sites, the teacher can further demonstrate and explain the
subjects and explore the pedagogical benefits and challenges of moving class participation
into the online environment.
http://faraday.physics.utoronto.ca/GeneralInterest/Harrison/Flash/
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http://www.phys4arab.net/vb/showthread.php?t=28517
‫" سلسلة المساعد ملتقى الفيزيائيين العرب "فالشات‬2
http://www.usd.edu
http://www.gcsescience.com/pwav32.htm
Note:
These modules were written by a teacher, for teachers, to provide the kind of
background information that makes the teaching of physics easier and better.
Assist Prof. Dr. Ali Hassan Ahmed
Dept. of Physics, College of Science
University of Salahaddin-Erbil
E-mail: aha66sara@yahoo.com, aha66sara@uni-sci.org
Mobile: +964 (0)750 461 1899
Further work was done for UNESCO by the Centre for Mathematics Science and Technology
Education in the Faculty of Education at the University of Alberta. Suggestions for further
work on this unit are appreciated. "'Biancoli, Alberto'" <a.biancoli@unesco.org>
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